Port fuel direct injection (PFDI) engines are capable of advantageously utilizing both port injection and direct injection of fuel. For example, at higher engine loads, fuel may be injected into the engine using direct fuel injection, thereby improving engine performance (e.g., increasing available torque and fuel economy). At lower engine loads, fuel may be injected into the engine using port fuel injection, thereby reducing vehicle emissions, NVH, and wear of the direct injection system components, (e.g., injectors, DI pump solenoid valve, and the like). In PFDI engines, the low pressure fuel pump supplies fuel from the fuel tank to both the port fuel injectors and the direct injection fuel pump. Because there may be periods of engine operation during which the direct injection fuel pump may not be running (e.g., during port fuel injection at low engine loads), lubrication of the DI fuel pump may not be maintained and wear, NVH and degradation of the DI fuel pump may be increased.
Conventional methods of operating PFDI engines may include direct injecting fuel at engine idle conditions in order to maintain lubrication of the direct injection fuel pump. Furthermore, in some PFDI engines, the low pressure fuel pump may be operated at excessive power levels in order to ensure robust supply of fuel to the direct injection pump and in order to mitigate direct injection pump cavitation. Other methods of operating PFDI engines attempt to optimize the low pressure fuel pump power consumption.
The inventors herein have recognized potential issues with the above approaches. First, because the direct injection fuel pump may not be used at low and idle engine loads in PFDI engines, pump lubrication may be reduced, thereby accelerating pump degradation. Furthermore, operating the direct injection pump during engine idle conditions can result in excessive NVH due to ticks generated by the DI fuel pump and due to a lack of engine noise to mask the pump noise. Second, conventional methods of controlling the low pressure fuel pump expend excessive pump power, thereby reducing fuel economy and pump durability, or do not robustly deliver fuel to the direct injection fuel pump, thereby causing pump cavitation, which may reduce engine performance and aggravate injection pump degradation.
One approach that at least partially overcomes the above issues and achieves the technical result of increasing direct injection pump durability without increasing NVH, and increasing robustness of fuel delivery to the direct injection fuel pump while reducing power consumption and without reducing low pressure pump durability, includes a method for a PFDI engine, during a first condition, comprising direct-injecting fuel to the PFDI engine, estimating a fuel vapor pressure, and setting a fuel lift pump pressure greater than the fuel vapor pressure by a threshold pressure difference, and during a second condition, comprising port-fuel-injecting fuel to the PFDI engine, setting a DI fuel pump duty cycle to a threshold duty cycle without supplying fuel to a DI fuel rail.
In another embodiment, a method of operating a fuel system for an engine comprises maintaining a fuel lift pump pressure greater than an estimated fuel vapor pressure while fuel is being direct-injected to the engine, and enforcing a DI fuel pump duty cycle above a threshold duty cycle even when fuel is not being direct-injected to the engine.
In another embodiment, an engine system comprises a PFDI engine, a DI fuel pump, a fuel lift pump, and a controller, comprising executable instructions to during a first condition, comprising direct-injecting fuel to the PFDI engine, estimating a fuel vapor pressure, and setting a pressure of the fuel lift pump greater than the fuel vapor pressure by a threshold pressure difference, and during a second condition, comprising port-fuel-injecting fuel to the PFDI engine, setting a DI fuel pump duty cycle to a threshold duty cycle without supplying fuel to a DI fuel rail.
In this way, DI fuel pump cavitation can be reduced, enabling the DI fuel pump to maintain operation at full volumetric efficiency while reducing lift pump power and thereby increasing robustness of DI fuel pump operation. Furthermore, DI fuel pump NVH and degradation of the DI fuel pump may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.